The present invention relates to a laser beam machining apparatus, and more particularly to a laser beam machining apparatus with an improved optical scanner control circuit.
Laser beam machining apparatus conventionally used for the trimming of thick film resistors or like purposes are typically constructed as illustrated in FIG. 1, wherein a laser beam 11 is permitted to pass a shutter 13 when a logical "1" signal is fed to its input terminal 154 and is blocked by the shutter 13 when a logical "0" signal is given fed thereto. A scanning circuit 9 generates digital signals indicative of the quantities of shift towards coordinates (X.sub.1, Y.sub.1) on the XY plane 19 of a surface to be machined. On input terminals 151 and 152 are set the quotients of the division of the coordinates (X.sub.1, Y.sub.1) on the XY plane 19 of the surface to be machined by the respective position resolving powers of optical scanners corresponding to the minimal quantities of shift. These digital quantities are converted to analog values in a scanner driving circuit 20 to drive an X-axis optical scanner 15 and Y-axis optical scanner 16. The laser beam 11 incident on both the X-axis optical scanner 15 and on the Y-axis optical scanner 16 is focused by a scanning lens 17, by way of a totally reflective mirror 6, on the surface to be machined.
FIG. 2 illustrates the action of the conventional laser beam machining apparatus on the XY plane 19 of the surface to be machined. The position resolving powers of the X-axis optical scanner 15 and Y-axis optical scanner 16 are assumed to be 10 .mu.m each, if a value of X.sub.1 /10 is fed to the input terminal 151 of the scanning circuit 9 and another value of Y.sub.1 /10 to the input terminal 152 of same, the laser beam 11 will be caused by the optical scanners 15, 16 to scan the XY plane 19 of the surface to be machined until it reaches the coordinates (X.sub.1 /Y.sub.1), where it will stop. Then, when the value of X.sub.1 /10 is fed to the input terminal 151 of the scanning circuit 9 and another value of Y.sub.2 /10 to the input terminal 152 of same, said laser beam 11 will scan the XY plane 19 of the surface to be machined from the coordinates (X.sub.1 /Y.sub.1) to another pair of coordinates (X.sub.1, Y.sub.2) thereon, and stop at the latter.
Then, by feeding a value of X.sub.2 /10 to the input terminal 151 of the scanning circuit 9 and another value of Y.sub.2 /10 to the input terminal 152 of same, said laser beam 11 is caused to scan the XY plane 19 of the surface to be machined from the coordinates (X.sub.1, Y.sub.2) to coordinate (X.sub.2, Y.sub.2), where it stops. Reference numerals 30 and 31, respectively, represent the scanning range and the scanning locus of the laser beam 1 on the XY plane 19 of the surface to be machined, and 32 presents the area of the workpiece 27 to be laser beam-machined on the surface to be machined.
Laser beam machining of a workpiece 27 is accomplished according to a timing chart shown in FIG. 3. P1, P2 and P3 are input signals to the input terminals 151 and 152 of the scanning circuit 9 and the input terminal 154 of the shutter 13, respectively. Unless the optical scanners 15, 16 drift due to temperature variation, machining will be achieved as represented by reference numeral 32 in FIG. 4. However, as optical scanners in any practical situation are subject to temperature drift, there will be a deviation on the XY plane 19 of the surface to be machined from the prescribed coordinates. Therefore, in trimming thick film resistors or the like, temperature drift will make it impossible for the laser beam machining of the workpiece to be accomplished in area 32, and instead causes it to take place either in area 33 or 34 (FIG. 4), inviting an insufficient accuracy of the thick film resistance or some other defects in the product.